The present invention relates to an allocation method for a tire pressure monitoring system in motor vehicles combining directly and indirectly monitoring tire inflation pressure.
Systems which enhance the active or passive safety are used at an increasing rate in up-to-date vehicles. As experience shows, many accidents are caused by defective vehicle tires. A large number of these tire defects are due to a wrong tire inflation pressure or a stealthy inflation pressure loss in the tire. Therefore, it is of great significance in terms of safety of the vehicle to reliably monitor the tire inflation pressure.
Two types of tire inflation pressure monitoring systems have become known so far. On the one hand, so-called directly measuring tire pressure monitoring systems (TPMS: Tire Pressure Monitoring System) as described e.g. in DE 199 26 616 C2 or in DE 199 38 431 C2, and so-called indirectly measuring tire pressure monitoring systems (DDS: Deflection Detection System) as described e.g. in DE 100 58 140 A1 are known in the art.
The tire pressure monitoring system with direct measurement (TPMS) measures the respective tire inflation pressure by means of pressure modules directly in the tire concerned, with the result that all wheels are monitored irrespective of each other. The measured tire inflation pressure is sent alone or in conjunction with other measured values (e.g. temperature of the tire) to one or more receiving units arranged at the vehicle, using a transmitting unit which is connected to the pressure measuring module. In this respect, each transmitting unit includes an individual identification code which is sent together with the measured tire inflation pressure and any possible other measured values. The receiving unit which is provided one time or several times relays the data received (measured values and identification codes) to an evaluating device which emits a warning to the driver when tire pressure loss prevails. The direct measurement of the tire inflation pressure permits the directly measuring tire pressure monitoring system (TPMS) to detect tire inflation pressure loss at a very early time already.
The directly measuring tire pressure monitoring system known in the art suffers from the shortcoming that the reliability is very limited on account of the fact that the pressure measuring modules usually are not designed redundantly, on the one hand, while, on the other hand, great expenditure is needed for detecting which tire (e.g. front left tire) suffers from a loss in inflation pressure, because several receiving units are generally necessary to this end in order to achieve a safe allocation of the tires to the installation positions (e.g. front left).
The tire pressure monitoring system with indirect measurement (DDS) is based on the measurement of rotational wheel speeds. The increase in rotational wheel speeds is a standard of the tire inflation pressure because a tire having a lower tire inflation pressure (e.g. 1.0 bar) that differs from the nominal pressure (e.g. 2.0 bar) exhibits a smaller dynamic rolling circumference. Due to this difference in rotational speeds, the tire pressure monitoring system with indirect measurement (DDS) detects tire inflation pressure loss. To determine the rotational wheel speeds, typically those wheel sensors are used which are already provided in a vehicle with an anti-lock system (ABS). These wheel speed sensors are favorable because they are monitored in terms of possible malfunctions or are designed redundantly, with the result that tire inflation pressure loss is detected with a high rate of reliability. As the installation position (e.g. front left) of the wheel sensors is known to the tire pressure monitoring system with indirect measurement (DDS), the allocation of a wheel with tire inflation pressure loss to its installation position is simple. Further, this system is very moderate in price because the necessary wheel sensors are already mounted at least in vehicles equipped with ABS.
It is disadvantageous in the known tire pressure monitoring system with indirect measurement (DDS) that a simultaneous tire inflation pressure loss on all wheels cannot be detected because a difference in the rotational speeds of the wheels cannot be detected in the event of a simultaneous tire inflation pressure loss.
Further, there are combined tire pressure monitoring systems linking a tire pressure monitoring system with direct measurement to a tire pressure monitoring system with indirect measurement. A combined tire pressure monitoring system of this type is described in DE 101 52 338 A1. The prior-art combined tire pressure monitoring system, for cost reasons, manages without taking into account the individual identification code, which is usually sent along with the measured tire inflation pressure and any possible other measured valued from the transmitting unit connected to the pressure measuring module to the receiving unit. It is disadvantageous in this arrangement that in case two or more vehicles are placed side by side, the evaluating device is unable to identify which tire inflation pressure sent belongs to the own vehicle.
In view of the above, an object of the invention is to provide an allocation method for a combined tire pressure monitoring system which permits a low-cost and reliable allocation of the vehicle wheels to the respective installation positions.